When it comes to relationship compatibility, we usually focus on the big things: religion, political views, and whether or not to have children. But a new study suggests we might want to put more weight on what seem like insignificant differences, such as preferring Pepsi when our partner would rather drink Coke.

Researchers at Duke University found that being partial to a different brand than your partner could affect relationship happiness more than other interests or personality traits.

"People think compatibility in relationships comes from having similar backgrounds, religion or education," said study co-author Dr. Gavan Fitzsimons, Ph.D, marketing professor at Duke University's Fuqua School of Business, in a statement. "But we find those things don't explain how happy you are in life nearly as much as this notion of brand compatibility."

The team found that the person who had the least power in the relationship, in part because they had no control in changing the other’s behavior, felt stuck with their significant other’s preferences. Dr. Danielle Brick, Ph.D, one of the study co-authors, explains that over time, these small injustices add up.

"If you are lower in relationship power and have different brand preferences than your partner, you're probably going to find yourself stuck with your partner's favorite brands, over and over again. This could lead to a death-by-a-thousand-cuts feeling," Brick said in a statement. "Most couples won't break up over brand incompatibility, but it leads to the low power partner becoming less and less happy."

And it’s not just soda preference that matters. Brand tastes for coffee, chocolate, beer, and cars were tested with the same results.

So, can something as small as what coffee you brew in the morning really stir up more conflict than religious differences? Brick says no, but that larger issues tend to be dealt with upfront while people ignore these small annoyances.

"If you are a different religion than your romantic partner, you know that if this is an issue you can't work through, then the relationship isn't going to last," Brick said. "Conversely, if you like Coke and your partner likes Pepsi, you're probably not going to break up over it -- but 11 years into a relationship, when he or she keeps coming home with Pepsi, day in and day out, it might start to cause a little conflict. And if you're the low-power person in the relationship, who continually loses out on brands and is stuck with your partner's preferences, you are going to be less happy."

Relationships are complicated, and scientists have long attempted to determine what makes people compatible. Dating website eHarmony tries to take the guesswork out by matching couples on 18 factors they believe make for happy relationships. According to the website, this was created from data from more than 200,000 people over 35 years. Included on their list are the bigger questions like religious, social and relationship values (preference for dark versus light chocolate won’t be found here). Still, scientists from this study think it might be a good idea to go ahead and name drop before you get serious.